This invention relates to an improved automobile transmission of the type having a reverse gear on the drive shaft which cooperates with a shift gear axially displaceable on a stationary axle.
In automobile transmissions of this type, the shift gear is rotatable on the stationary axle and is axially displaceable along the stationary axle to move into and out of engagement with the reverse gear. When shifted into reverse, the shift gear first engages the reverse gear, which is on the drive shaft, and once having engaged the reverse gear, with further axial displacement, engages a counter gear wheel fixed on the transmission output shaft.
When the shift gear engages first the reverse gear, and also secondly the counter gear on the output shaft, however, noises and shifting shocks may occur. Since the drive shaft is coupled to the engine, it will rotate with the engine as long as the clutch is engaged. Even after the clutch is disengaged to shift into reverse, however, the drive shaft and reverse gear will continue rotating due to inertia. Thus the rotating reverse gear has to mesh with the stationary shift gear, which will cause gear grinding. Moreover, once engaged, the reverse gear will cause the shift gear to rotate. Since the automobile and thus output shaft are normally stationary when shifting into reverse, once again a rotating gear (shift gear) engages a stationary gear (counter gear on the output shaft), which results in grinding.
In commonly owned U.S. patent application Ser. No. 961,773, filed Nov. 17, 1978, an arrangement for a noiseless engagement of the shift gear with the counter gear is disclosed, in which a synchronizing device is provided on the shaft to brake the rotation of the shift gear before it engages the counter gear. An arrangement for eliminating the shifting noises between the shift gear and the reverse gear is also proposed wherein the two gears are permanently engaged.
While this eliminates shifting noises between the reverse gear and the shift gear, the axial enlargement (width) of the reverse gear needed to effect such an arrangement is difficult in practice to manufacture. The reverse gear is formed by a gear shaper cutter which cuts the gear out of the drive shaft. In order to do so, a sufficiently wide relief groove is needed on at least one side of the gear, at least in the engaging area of the adjacent gear, which relief groove would no longer be available if the width (axial length) of the reverse gear were enlarged, as would be required if the reverse gear were to engage the shift gear through the entire axial displacement of the shift gear. Moreover, the constant meshing of the shift gear with reverse gear, as would then occur in all operating states of the engine, whether forward or reverse, itself generates considerable noise and is thus undesirable.